Ti2AlC MAX Phase Research Articles

Investigation of possibility of fabrication of long-length samples of Ti3AlC2–Al MAX-cermet by the SHS method with spontaneous infiltration by aluminum melt

The article discusses the features of combining the self-propagating high-temperature synthesis (SHS) of the Ti3AlC2 MAX phase porous skeleton with infiltration by aluminum melt in a spontaneous mode in order to obtain enlarged samples of Ti3AlC2–Al ceramic-metal composite (MAX cermet) in an air atmosphere. A new scheme was developed for obtaining long-length SHS cermet samples from a bulk density charge with spontaneous infiltration by melt in the same direction with the combustion wave movement, which makes it possible to regulate the time gap between the end of the Ti3AlC2 synthesis and the beginning of the spontaneous pore filling with aluminum melt. This technology was used to obtain a Ti3AlC2 SHS skeleton with a total length of 250 mm and a diameter of 22–24 mm where the depth of infiltration with pure aluminum was about 110 mm, and impregnation with the Al–12%Si alloy was 130 mm. The paper provides comparative data on density, microstructure, and phase composition at different areas along the length of MAX cermet samples obtained. It was found that infiltration with pure aluminum destroys the Ti3AlC2 MAX phase to transform it into a mixture of TiC + TiAl3 phases in the SHS cermet, and 12 % Si added to the Al melt promote Ti3AlC2 preservation in the cermet to a some extent. Instead of MAX cermet samples with the target composition of Ti3AlC2–Al and Ti3AlC2–(Al–12%Si), long-length samples of SHS cermets with a different actual phase composition were obtained: TiC–TiAl3–Al and TiC–Ti3AlC2–TiAl3–(Al–12%Si), respectively, where the Ti3AlC2 MAX phase either practically absent or present in small quantities. The average hardness values of TiC–TiAl3–Al and TiC–Ti3AlC2–TiAl3–(Al–12%Si) SHS cermets wereHB= 640 and 740 MPa, density ρ = 2.88÷3.16 g/cm3 and 3.03÷3.13 g/cm3, and residual porosityП= 17.0÷24.6 % and 17.6÷20.3 %, respectively.

A facile pot synthesis of (Ti3AlC2) MAX phase and its derived MXene (Ti3C2Tx)

Various processing techniques reported in the literature for synthesizing the Ti3AlC2 MAX phase involve high calcination temperature, expensive equipment, and inert environmental requirement. Here, we report a cost-effective, solid-state, single-step synthesis route of the Ti3AlC2 MAX phase. Optimizing the stoichiometry of the precursors and controlling the thermal treatment, the desired MAX phase has been attained, as confirmed by XRD analysis. Further, Ti3C2Tx (where, Tx: O, OH, F functional groups) MXene was prepared from this one-pot synthesized MAX phase. FESEM, TEM, and Raman spectroscopy were used to ensure that the hexagonal structure of the MAX phase was retained in as-synthesized MXene. Further, XPS was employed to detect the presence of surface functional groups (-O, –OH, and –F) on the MXene surface. UV–vis spectroscopy shows a strong absorption peak in the NIR region.

A theoretical investigation of the effect of Ga alloying on thermodynamic stability, electronic-structure, and oxidation resistance of Ti2AlC MAX phase

We present a systematic investigation of thermodynamic stability, phase-reaction, and chemical activity of Al containing disordered Ti2(Al-Ga)C MAX phases using machine-learning driven high-throughput framework to understand the oxidation resistance behavior with increasing temperature and exposure to static oxygen. The A-site (at Al) disordering in Ti2AlC MAX (M=Ti, A=Al, X=C) with Ga shows significant change in the chemical activity of Al with increasing temperature and exposure to static oxygen, which is expected to enable surface segregation of Al, thereby, the formation of Al2O3 and improved oxidation resistance. We performed in-depth convex hull analysis of ternary Ti–Al–C, Ti–Ga–C, and Ti–Al–Ga–C based MAX phase, and provide detailed contribution arising from electronic, chemical and vibrational entropies. The thermodynamic analysis shows change in the Gibbs formation enthalpy (ΔGform) at higher temperatures, which implies an interplay of temperature-dependent enthalpy and entropic contributions in oxidation resistance Ga doped Ti2AlC MAX phases. A detailed electronic structure and chemical bonding analysis using crystal orbital Hamilton population method reveal the origin of change in phases stability and in oxidation resistance in disorder Ti2(Al1−xGax)C MAX phases. Our electronic structure analysis correlate well with the change in oxidation resistance of Ga doped MAX phases. We believe our study provides a useful guideline to understand to role of alloying on electronic, thermodynamic, and oxidation related mechanisms of bulk MAX phases, which can work as a precursor to understand oxidation behavior of two-dimensional MAX phases, i.e., MXenes (transition metal carbides, carbonitrides and nitrides).

Ultralarge Flakes of Ti3C2Tx MXene via Soft Delamination.

Two-dimensional (2D) titanium carbide MXene (Ti3C2Tx) has attracted significant attention due to its combination of properties and great promise for various applications. The size of the 2D sheets is a critical parameter affecting multiple properties of assembled films, fibers and 3D structures. The increased lateral size of MXene flakes can benefit not only their assemblies by improving the interflake contacts and alignment but also fundamental studies at the individual flake level, allowing for facile patterning and investigation of intrinsic physical properties of MXenes. Increasing the average size of the parent MAX phase is one of the strategies previously used to increase the flake size of the resultant MXene. Here, we show that the protocol used for the next step of the synthesis procedure, delamination of multilayer MXene into individual nanosheets, significantly affects the lateral size of the resultant flakes. We developed a soft delamination approach, which prevents fracture of flakes and preserves their size. Combining this approach with the large-grain Ti3AlC2 MAX phase precursor, we achieved individual flakes of up to 40 μm in lateral size. These flakes can be used for patterning multiple contacts and fabrication of field-effect transistors for multiprobe electrical characterization and other measurements. These findings indicate the importance of controlling the delamination process in order to achieve large MXene flakes and improve properties of MXene-based materials and devices.

Role of Ti3AlC2 MAX phase on characteristics of in-situ synthesized TiAl intermetallics. Part IV: mechanical properties

In this study, the 4th part of a series of publications on the sintering and characterization of TiAl-Ti3AlC2 composite materials, the mechanical properties were measured and discussed. For this purpose, different contents of synthesized Ti3AlC2 reinforcement (10, 15, 20, 25, and 30 wt%) were added to metallic Ti and Al powders, then ball-milled and manufactured by spark plasma sintering (SPS) for 420 s at 900 ºC under 40 MPa. Flexural strength, fracture toughness and Vickers hardness were measured by 3-point technique, SENB method, and indentation technique, respectively. Increasing the Ti3AlC2 content resulted in improvement of the mechanical properties, so that TiAl-25 wt% Ti3AlC2 composite showed the best flexural strength and Vickers hardness (270 MPa and 4.11 GPa, respectively). Increasing amount of Ti3AlC additive had no significant effect on fracture toughness. Densification improvement, in-situ formation of Ti2AlC, and limitation of grain growth were recognized as the reasons of mechanical properties enhancement. In contrast, further addition of Ti3AlC2 (30 wt%) decreased the mechanical properties due to the reduction of density and formation of more Ti2AlC agglomerates in grain boundaries.

Preparation of Au/Pt/Ti3C2Cl2 nanoflakes with self-reducing method for colorimetric detection of glutathione and intracellular sensing of hydrogen peroxide

A novel two-dimensional nanolayered Ti3C2Cl2 MXene material derived from MAX phase was synthesized through a HF-free method based on elemental replacement reaction in the A atom of traditional Ti3AlC2 MAX phase and ZnCl2 molten salts, which possess large specific surface areas, excellent electric conductivity and reducing property. Then the Au/Pt bimetallic nanoparticles decorated Ti3C2Cl2 nanoflakes were synthesized by a self-reduction method with Ti3C2Cl2 as a natural reducing agent and supporter, which possess peroxidase mimic activity and oxidase mimic activity, simultaneously. Based on the prominent catalytic activity of Au/Pt/Ti3C2Cl2 nanocomposite, a novel colorimetric platform was developed for in situ sensing of hydrogen peroxide (H2O2) released from live HeLa cells and colorimetric detection of glutathione (GSH), with the detection ranges of 50–10000 μM and 0.1–20 μM, the detection limits were 10.24 μM and 0.07 μM, respectively. These results allow utilization of the easily accessible 2D surface for the design and application of 2D layered material-supported MXene nanocomposites catalysts in intracellular biosensing.

Parameters of the Unit Cell of the Ti3AlC2 MAX‐Phase with Hydrogen

Investigations of the penetration of hydrogen into ternary carbides (the so‐called MAX phases) become topical because it has been found recently that these materials can be protective coatings. Herein, near‐surface layers of two bulk samples of the Ti3AlC2 MAX phase are saturated electrolytically several times by hydrogen. Parameters of the hexagonal unit cell are measured by means of X‐ray diffractometry after each saturation of the same sample. It is found that the increase in the distance between the base planes of the unit cell is ten times larger than the increase of the side of the unit cell in the base plane. The estimated amount of hydrogen that remains in the lattice at room temperature is about 1.6% (at). It is found that the sample can be saturated by hydrogen up to 3% (at), but the lattice relaxes with time. The relaxation time for the distance between base planes is about 60% of that for the side of the lattice in the base plane.

In situ oxygen doped Ti3C2Tx MXene flexible film as supercapacitor electrode

Heteroatom doping has been proven to be an effective strategy to improve the electrochemical energy storage capacity of two-dimensional MXenes. However, the heteroatom for MXenes is mainly focused on the N atoms, while the effects and underlying mechanisms of O substituted partial C atoms of MXene have not been explored so far. Herein, comprehensive research is firstly performed to reveal the oxygen doping mechanism in Ti3C2Tx MXene by the experimental characterization and the density functional theory simulation. The in situ oxygen doped Ti3C2Tx nanosheets, in which oxygen atoms substitute partial carbon atoms in the titanium octahedron, are synthesized by etching the oxygen doped Ti3AlC2 MAX phase, which is more facile than the complex post-doped process. The introduction of appropriate oxygen atoms can effectively improve the interlayer space, electronic conductivity, and interface charge transfer of the Ti3C2Tx MXene as a supercapacitor electrode. Further, the electrochemical performances demonstrate that the oxygen doped MXene (O-Ti3C2Tx-0.05) film electrode can deliver a higher capacity of 306.0 C g−1 compared to the pristine Ti3C2Tx electrode (216.8 C g−1). Besides, the quantitative analysis results imply that the enhanced capacitance is mainly attributed to the diffusion-controlled capacitance and interface capacitance, which result from the higher Ti metal active center, the enhanced quantum capacitance, and the higher adsorption energy.

Formation of Bulk Samples from the Ti3AlC2 MAX-Phase Powder by Selective Laser Sintering

Formation of Bulk Samples from the Ti3AlC2 MAX-Phase Powder by Selective Laser Sintering

Deposition of Ti2AlC MAX phase onto the side polished fiber as saturable absorber for soliton mode-locked fiber laser generation

Deposition of Ti2AlC MAX phase onto the side polished fiber as saturable absorber for soliton mode-locked fiber laser generation

Core structure and Peierls barrier of basal edge dislocations in Ti[formula omitted]AlC[formula omitted] MAX phase

In the MAX phase, the nucleation and motion of basal dislocations dominate the plastic deformation at room temperature. Therefore, information on the dislocation core properties and energy barrier for dislocation glide is essential to understand their plasticity. Dislocations in MAX phases are mainly 〈a〉-type basal edge dislocations (b=a/3[112̄0]) and can glide in the basal plane (typical slip) or form kink bands depending on the load direction and crystal orientation owing to the strong plastic anisotropy. In this study, we determined the core structure, Peierls barrier, and corresponding stress of a/3(0001)[112̄0] edge dislocations in Ti3AlC2 MAX phase by multiple computational approaches using the semidiscrete variational Peierls–Nabarro method, density functional theory, and classical bond-order-potential-based molecular statics calculations. The a/3[112̄0] basal edge dislocation was dissociated into two Shockley partial dislocations with a 2–2.5b-wide stacking fault in between. These partial dislocations glide between the Ti(4f) and Al atomic layer. For straight dislocation motion, the Peierls barrier was single-humped and the corresponding Peierls stress was estimated to be approximately 182 MPa.

A Facile Etching Route for Preparing Ti3C2 MXene with Enhanced Electrochemical Performance in Silver Nitrate Solution

Two-dimensional Ti3C2 MXene is a promising electrode material for high-capacity supercapacitor, which is normally prepared by selective etching of the Al layer from ternary carbide Ti3AlC2 MAX phase using HF acid solution. Here a distinct etching method using a little HF acid is reported. Ti3C2 MXene decorated with Ag nanoparticles are synthesized via a chemical replacement reaction with AgNO3 solution at room temperature and then evaluated as working electrodes. Due to the synergistic effect between Ag and Ti3C2 matrix, the resulting composite of the 10 wt% AgNO3 treated sample (Ag-10) exhibits higher specific capacitance of 779.5 F g−1 at the scan rate of 5 mV s−1 in 6 M KOH electrolyte solution and shows good cycling stability with capacitance retaining 95% after 5000-cycles. This work also shows the possibility of using other metallic cations with higher redox potential to prepare high performance MXenes for supercapacitor materials.

Role of Ti3AlC2 MAX phase on characteristics of in-situ synthesized TiAl intermetallics. Part III: microstructure

In this paper, the 3rd part of a series of publications on the sinterability and characteristics of TiAl–Ti3AlC2 composites, the microstructure development during the synthesis and sintering processes was studied by scanning electron microscopy (SEM). Chemical evaluation of various phases in the developed microstructures was performed using energy-dispersive X-ray spectroscopy (EDS) in different ways such as point, line scan and two-dimensional elemental map analyses. For this purpose, five samples were fabricated with different percentages of Ti3AlC2 MAX phase additive (10, 15, 20, 25 and 30 wt%). Ball-milling and spark plasma sintering (SPS: 900 °C/7 min/40 MPa) of as-purchased Al and Ti powders with already-synthesized Ti3AlC2 additive were selected as composite making methodology. SEM/EDS analyses verified the in-situ manufacturing of TiAl/Ti3Al intermetallics as the matrix during the SPS process and the presence of Ti3AlC2 as the ex-situ added secondary phase. Moreover, the in-situ synthesis of Ti2AlC, another member of MAX phases in Ti-Al-C system, was also detected in titanium aluminide grain boundaries and attributed to a chemical reaction between TiC (an impurity in the initial Ti3AlC2 additive) and TiAl components.

Ti3AlC2/Pd Composites for Efficient Hydrogen Production from Alkaline Formaldehyde Solutions.

Research on catalytic oxidation in a promising but mild manner to remove formaldehyde and produce hydrogen is rarely reported. Here, the use of the Ti3AlC2 MAX phase as support for palladium nanoparticles was explored for the hydrogen generation from alkaline formaldehyde solution at room temperature. The results showed that Ti3AlC2/Pd catalyst with 3 wt% Pd loading had a much higher capability for hydrogen production than conventional Pd nanoparticles. In addition, by further optimizing the formaldehyde concentration, NaOH concentration, and the reaction temperature, the hydrogen production rate could be further increased to 291.6 mL min−1g−1. Moreover, the obtained apparent activation energy of the Ti3AlC2/Pd catalyzed hydrogen production reaction is 39.48 kJ mol−1, which is much lower than that of the literature results (65 kJ mol−1). The prepared Ti3AlC2/Pd catalysts as well as the catalytic process could act as a “two birds with one stone” effect, that is, they not only eliminate noxious formaldehyde but also generate clean hydrogen.

Isothermal Oxidation of Ti3Al0.6Ga0.4C2 MAX Phase Solid Solution in Air at 1000 °C to 1300 °C

The atomically laminated Ti2AlC, Ti3AlC2 and Cr2AlC MAX phases, with A = Al, form adherent, passivating α-alumina, Al2O3, oxide scales when heated in air. The effect of solid solutions on the A layers in affecting the oxidation kinetics remains a subject of open research. Herein we synthesize a dense bulk polycrystalline Ti3Al1−xGaxC2 (x ≈ 0.4) solid-solution and investigate its isothermal oxidation in ambient air, in the 1000 °C–1300 °C temperature range, for times varying between 15 and 300 h. At 1000 °C, a passivating dense Al2O3 layer ( ≈ 1–2.6 μm thick) with near cubic kinetics and an overall weight gain that is slightly less than either Ti3AlC2 or Ti2AlC is formed. At 1200 °C, the Al2O3 layer thickens (3.5–12 μm thick) with some scale delamination on the corners initiating at 15 h. At 1300 °C, the Al2O3 layer (7.6–20.7 μm thick) wrinkles and Al2TiO5 forms. Though the Al2O3 grains coarsen at 1200 °C and 1300 °C, the weight gain is higher than that for Ti3AlC2 or Ti2AlC. At around 7 at. %, this is one of the lowest, if not lowest, Al mole fraction in a Ti-based alloy/compound that forms an Al2O3 passivating layer. We further provide compelling microstructural evidence, in the form of a duplex oxide, that at 1000 °C, the outward Al flux, JAl, and the inward O flux, JO, are related such that 2 JAl = 3 JO. A fraction of these fluxes combine, at the duplex oxide interface, to nucleate small grains

Formation of the Ti2Alc Max-Phase in a Hydride Cycle From a Mixture of Titanium and Aluminum Carbohydride Powders

Formation of the Ti2Alc Max-Phase in a Hydride Cycle From a Mixture of Titanium and Aluminum Carbohydride Powders

Synthesis of Ti3C2Tx MXene from the Ti3AlC2 MAX phase with enhanced optical and morphological properties by using ammonia solution with the in-situ HF forming method

Liquid phase exfoliation of Ti3C2Tx MXene using LiF/HCl mix, forming HF in situ, has been modified by the addition of NH4OH. The base assisted dilution and extraction of MXene enables a quick control over pH and improves the structural, morphological and optical properties of the compound. The formation of a buffer compound NH4F, reduces the oxidation on the surface of MXene and etches off the residual MAX phase, by attacking Al. The structural features of the prepared NH4OH added Ti3C2Tx MXene are remarkably better than the HF etched samples, with the characteristic MXene peak in XRD being emphasized in the former. The addition of ammonia solution improves the milder in situ HF etching technique, by giving the characteristic open accordion structure to the compound, making the compound easy to delaminate and more stable against oxidation in ambient atmosphere.

Functionally graded laminated composites fabricated from MAX-phase filled preceramic papers: Microstructure, mechanical properties and oxidation resistance

This paper describes the fabrication and characterization of novel preceramic paper-derived functionally graded materials (FGMs) based on Ti3(Si,Al)C2 MAX phase. The FGMs with different architecture were fabricated via spark plasma sintering of stacked preceramic papers at 1250 °C for 5 min. Microstructure, phase composition and elemental distribution were analyzed by scanning electron microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy, respectively. Oxidation tests were performed in air at 1300 °C for 5 h. FGMs containing Al- and Si-enriched MAX-phase layers were formed. The fabricated materials exhibit high flexural strength (over 600 MPa), which are dependent on microstructure and composition of individual layers as well as the architecture of composites. It was found that texturing of MAX phase grains during SPS results in anisotropic hardness of the composite. The difference in the composition of the individual layers also provides a hardness gradient in the composite. It was shown that the formation of the outer layer from the Al-enriched Ti3Al(Si)C2 MAX phase increases the corrosion resistance of Ti3SiC2-based composites. The high corrosion resistance of FGMs is due to the growth of a continuous and dense Al2O3 oxide layer.

Production and characterization of carbide-derived-nanocarbon structures obtained by HF electrochemical etching of Ti3AlC2

In this research, we propound a facile and efficient strategy for the synthesis of carbide-derived nanocarbon structures (CDCs) by electrochemical etching of Ti3AlC2 MAX phase in hydrofluoric acid solutions. Al, Ti and C powders were milled and used to synthesize Ti3AlC2 MAX phase powders and then, the obtained powders were sintered using spark plasma sintering (SPS) method. The obtained bulk sample was then electrochemically etched for 2 h at 5v and 20v and concentrations of 20 wt% and 10 wt% hydrofluoric acid to obtain CDC. The results showed that titanium and aluminum were extracted from the Ti3AlC2 MAX phase structure by electrochemical etching in HF solution. Structural and morphological studies of CDCs obtained by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and scanning field emission electron microscopy (FESEM) were performed. Examination of SEM and FESEM illustrations showed that the structure of CDCs consisted of graphene nanosheets. The distance and number of graphene layers were obtained according to the XRD results and the ID/IG value was assessment to be 0.81 according to Raman spectroscopy, demonstration plenty of oxygen functional groups on the surface of graphene sheets. Also, EDS analysis and XRD and Raman spectroscopy outcomes were in well agreement with SEM and FESEM images. The results were shown, at constant voltage, increasing the concentration has led to the production of more CDC nanostructures. At a constant concentration with increasing voltage amorphous carbon was formed instead of graphite. Eventually it was found that by changing the voltage and concentration of the solution, both titanium and aluminum were still extracted and CDC was formed.

Исследование перспективных жаростойких покрытий систем Y-Al-O и Ti-Al-C

The paper describes the results of studies of the phase composition of heat-resistant coatings based on the Ti-Al-C system and the Y-Al-O system using X-ray diffraction analysis. Coatings were deposited on molybdenum samples by cathodic-arc deposition from two single-component titanium and aluminum cathodes in acetylene and argon gas mixture. The results of the study of the phase composition showed that, after deposition, the coatings of both systems have an amorphous structure. After heat treatment, in the Ti-Al-C system coating the MAX phase Ti2AlC is formed as well as Ti-Al intermetallic compounds, in the coating of the Y-Al-O system, oxides Y2O3, YAlO3, Y4Al2O9 are formed.